#include <fstream>
#include <bitset>
#include <stack>
#include <vector>

using namespace std;

const int N = 1e5;
const int M = 5e5;

pair<int, int> e[M];
bitset <M> sters;
vector <int> a[N+1];
stack<int> stiva;
int poz[N+1], n, m;

bool este_euler()
{
    return true;
}

int caut_muchie(int x)
{
    for (int i = poz[x]; i < a[x].size(); i++)
    {
        if (!sters[a[x][i]])
        {
            poz[x] = i + 1;
            return a[x][i];
        }
    }
    return -1;
}

int main()
{
    ifstream in("ciclueuler.in");
    ofstream out("ciclueuler.out");
    in >> n >> m;
    for (int i = 0; i < m; i++)
    {
        int x, y;
        in >> x >> y;
        e[i] = {x, y};
        a[x].push_back(i);
        a[y].push_back(i);
    }
    in.close();
    if (!este_euler())
    {
        out << -1;
        out.close();
        return 0;
    }
    stiva.push(1);
    while (!stiva.empty())
    {
        int x = stiva.top();
        int muchie = caut_muchie(x);
        if (muchie == -1)
        {
            stiva.pop();
            if (!stiva.empty())
            {
                out << x << " ";
            }
        }
        else
        {
            int y = e[muchie].first + e[muchie].second - x;
            stiva.push(y);
            sters[muchie] = 1;
        }
    }
    return 0;
}